1. Field of the Invention
The present invention relates to a multifilament superconducting wire of Nb.sub.3 Al, which can be applied to a superconducting wire for a nuclear fusion reactor or SMES, for example.
2. Description of the Background Art
A superconductive material of Nb.sub.3 Al, having a high critical magnetic field which is said to be in excess of 30T and a distortion property which is superior to that of Nb.sub.3 Sn, is expected as the third practical superconductive material following NbTi and Nb.sub.3 Sn, particularly as a wire material for a superconducting magnet for a nuclear fusion reactor.
It has recently been reported that the critical current density of an Nb.sub.3 Al superconducting wire is increased to a level which is equivalent to or higher than that of Nb.sub.3 Sn when Nb and Al parts thereof are reduced to about 0.1 .mu.m in thickness.
However, it has been impossible to obtain a long superconducting wire of Nb.sub.3 Al since elongation of the Nb.sub.3 Al superconductive material is industrially difficult due to inferior workability of Nb and Al. Although attempts have been made to elongate Nb.sub.3 Al materials into long wire by a jelly roll method, an Nb pipe method and the like, no satisfactory results have been obtained. For example, a length of at least 600 m is required for wire which is applied to a superconducting magnet for a nuclear fusion reactor, and a length of at least 1000 m is currently desired as the target of elongation. While some attempts have been made to prepare a wire with sheath of Cu-10%Ni, it is necessary to use a stabilizing material of Cu.